Apparatus for the vaporization of formamide



April 30, 1935. H. A. BOND APPARATUS FOR THE VAPORIZATION OF FORMAMIDE Original Filed July 9, 1931 INVENTOR. Harlan A. Bond A TTORNEY.

- the drawing! mada -Juices UNITED STATES Harlan A. Bond,

E. I. du Pont Original application July 9, 1931,

Niagara Falls, N. Y., assignor to de Nemours &

gton, DeL,

Company, Incora corporation of Serial No.

549,585. Divided and this application November 18, 1933, Serial No.

'1 Claim.

This invention relates to the vaporization of formamide-and more particularly to the vapori zation of formamide from metal Vaporizers.

This application is a division of my copending application 8. N. 549,585; filed July 9, 1931.

Because of its high boiling point, around 200 C. at atmospheric pressure, and because of the decomposition of formamide into carbon monoxhis and ammonia, when heated, the problem of vaporizing formamide has heretofore presented considerable difiiculty. To avoid this decomposition it has previously been proposed to vaporize formamide at reduced pressure and it has further been proposed to vaporize formamide from surfaces heated above 215 C. without allowing the substantial accumulation of liquid formamide on the vaporizing surface. The heretofore proposed methods of vaporizing formamide are costly, require more or less. elaborate apparatus, necessitate careful control and therefore are not entirely satisfactory. Although the decomposition is small, solids stick to the hot surface and heat conduction becomes poor. Moreover, there is tendency when the liquid strikes the hot surface forit to agglomerate in droplets which evaporate with explosive effect and give uneven evaporation.

One object of this invention is to provide an apparatus for vaporizing accumulated liquid formamide from a metal surface without appreciable decomposition of the formamide and at t -tially atmospheric pressure. A further object of this invention is to simplify and improve the vaporizing of formamide. Further objects will be apparent hereinafter. 1

The invention comprises vaporizing formamide from a heat conducting surface upon which said formamide is allowed to accumulate in a shallow pool which covers a substantial portion of the surface. Metal surfaces are particularly useful since their rate of heat conduction is greater than that of other materials.

The accompanying drawing shows in cross-section one form of apparatus suitabiefor carrying out the process of this invention. Referring to is a metal base plate in which are embedded electrical heating elements 2. Metal cover 3, of such construction as to form a vapor space i6, is flanged on top of base plate I. 4 is an inlet pipe for liquid formamide having its terminus 5 within the cover 3 and close to the base plate I; 6 is an outlet pipe for formamide vapor; several openings as at I are provided in the base plate in which thermocouples or other temperature measuring (1 vices may be inserted;

B is a well of metal extending into the outlet tube into which a thermometer 9 is inserted.

The invention will now be further described in terms of the accompanying drawing.

Liquid formamide is flowed into the vaporizer through pipe 4 and spread as a shallow pool over a portion of the massive base plate i, which is heated by means of heating elements 2 to a temperature of preferably between about 200 to 400 C. The vaporizer is tilting or slope will or transverse spread of liquid and favor the formation of a shallow pool with its near the inlet end. It will be found in general that the shallow pool of liquid formamide may cover a substantial portion of the vaporizing surface and may cover the entire surface. The temperature of the vaporizer plate near will ordinarily be maintained at about the boiling point of formamide, while nearer the exit end the temperature may be considerably higher, it may attain 300 to 400 C., or even more, on those portilted or sloped toward the 10 deeper portions the inlet end tions of the vaporizer surface which are not covered by liquid. I prefer to vaporize at temperatures of 200-400 C.

To further clarify the invention, a specific example is given below, which however, should not be taken to limit details shown therein.

' Example An apparatus similar to drawing was employed consisting aluminum base plate 2" thick by 12" wide by 24" long. 12 nichrome heating elements extending transversely through the base, having a capacity of about 2 kilowatts each at 110 volts that mown in the the invention to the specific of a. forged were uniformly spaced lengthwise of the base plate and embedded therein. The formamide was introduced through an aluminum pipe /4" in diameter which terminated V," above the base plate 0. The outlet pipe for formamide va por was also aluminum and was 1%" Twothermocouples were inserted in the holes provided in the base plate of the vaporizer, one near the inlet end and a second beyond the edge of the liquid pool of formamide accumulated in the vaporizer. angle of about 2 toward the inlet end. The entire vaporizer was thoroughly insulated with powdered magnesia contained in a rectangular sheet iron shell surrounding the vaporizer.

A thermometer was inserted in diameter. 4 5

The apparatus was tilted at an in the well at the outlet end to measure the temperature of the formamide vapor produced. Liquid formamide was flowed into the apparatus at the rate of 142 grams per minute and formamide vapor collected therefrom at substantially the same rate. Vaporization was carried out at substantially atmospheric pressure. The temperature near the inletend and beneath the accumulated pool of formamide varied from 195 to 210 C. Tests indicated that about to of the vaporizing surface was covered by the liquid formamide. The average temperature of the vaporizer beyond the point occupied by the pool of formamide was 374 C. varying from 365 to 395 C. in a series of of measurements. The average temperature of the vapor in the outlet pipe was 280 C. This temperature is the average of several taken over a one hour period. Tests on the percentage decomposition of formamide in apparatus of this type have shown that the loss was in all cases less than 1.5% and frequently as low as 0.5%.

While the apparatus has been described as made of aluminum, other metals which do not deleteriously affect the decomposition of formamide, for example copper, brass, iron or steel may be used. A metal surface covered with an adherent non-reactive thin oxide layer, for example, ZnO or A1203 may also be used, subject to the same restrictions. Good heat conducting surfaces are preferable.

The dimensions of ranged to produce a uniform temperature over the vaporizing surface. I have found it advisable to so arrange them that when the apparatus is empty various parts of the vaporizing surface will not show more than 20 to 30 C. difference in temperature when heat is applied.

the rate of heat supply; if correct, this rate of heating should be such that should the formamide as remains on the surface will be completely evaporated within 5-10 min- The temperature may also be adjusted by eral exceed 400 C., i. e., the surface of the vaporizer will vary from about the boiling point of formamide up to about 400 C. The rate of heating should permit vaporization to take place at a sufficient rate so that the liquid formamide does erably not more than 12 minutes, since otherwise the rate of decomposition, which is of the order of 1 to 2% per minute, may become excessive.

The advantages of this process lie in its simplicity of operation and in the effective and speed; evaporation of formamide without substantial decomposition losses due to the formation of carbon monoxide and ammonia. It is particularly useful where a rapid supply of substantially pure formamide vapor is desired. It has been found to give excellent results when used in connection with a converter such as that described in U. S. P. 1,675,366, wherein said vapors are converted to hydrocyanic acid and water by a process requiring formamide of high purity.

I claim:

1. A vaporizer comprising a member having a vaporizing surface capable of being heated and sloping at an angle with the horizontal, a cover therefor adapted to provide a vapor space above said member, liquid supply means terminating adjacent to the sloping vaporizing surface of said member near the lowest point thereof, and vapor exit means leading from said cover.

2. A vaporizer comprising a-member having a sloping, substantially plane vaporizing surface, a cover therefor adapted to provide a vapor space above the vaporizing surface of said member, means for uniformly applying heat to the vaporizing surface of said member, a liquid supply means terminating close to the vaporizing surface of said member and near the lower end thereof and a vapor exit means leading from said cover.

3. A vaporizing apparatus comprising a relasloping metal vaporizing base plate having a vaporizing surface, heating elements uniformly embedded therein, a cover for 5. A vaporizing apparatus comprising a rela- I tively massive rectangular metal vaporizing base at an angle of about 2 from the horizontal, means for uniformly heating said plate, a cover form a shallow vapor the base plate is composed of aluminum.

HARLAN A. BOND. 

